refactor(function): well defining output value

Sources/Common/DataModel/Box/index.d.ts

@@ -37,9 +37,9 @@ export interface vtkBox extends vtkObject {
      * @param p1 
      * @param p2 
      * returns @object IBoxIntersections {t1, t2, x1, x2} object containing the t1, t2 parametric values and
-     * x1, x2 coordinates of the line intercept points in the bounding box
+     * x1, x2 coordinates of the line intercept points in the bounding box or undefined
      */
-    intersectWithLine(p1: Vector3, p2: Vector3) : IBoxIntersections;
+    intersectWithLine(p1: Vector3, p2: Vector3) : IBoxIntersections | undefined;
 
     /**
      * 
@@ -80,7 +80,7 @@ export function newInstance(initialValues?: IBoxInitialValues): vtkBox;
 // Bounding box intersection code from David Gobbi.  Go through the
 // bounding planes one at a time and compute the parametric coordinate
 // of each intersection and return the parametric values and the calculated points
-export function intersectWithLine(bounds, p1, p2): IBoxIntersections;
+export function intersectWithLine(bounds, p1, p2): IBoxIntersections | undefined;
 
 /**
  * vtkBox provides methods for creating a 1D cubic spline object from given